全文获取类型
收费全文 | 5471篇 |
免费 | 539篇 |
国内免费 | 245篇 |
专业分类
电工技术 | 440篇 |
综合类 | 366篇 |
化学工业 | 879篇 |
金属工艺 | 329篇 |
机械仪表 | 382篇 |
建筑科学 | 504篇 |
矿业工程 | 163篇 |
能源动力 | 220篇 |
轻工业 | 389篇 |
水利工程 | 108篇 |
石油天然气 | 266篇 |
武器工业 | 29篇 |
无线电 | 694篇 |
一般工业技术 | 586篇 |
冶金工业 | 240篇 |
原子能技术 | 62篇 |
自动化技术 | 598篇 |
出版年
2024年 | 26篇 |
2023年 | 90篇 |
2022年 | 200篇 |
2021年 | 231篇 |
2020年 | 168篇 |
2019年 | 141篇 |
2018年 | 164篇 |
2017年 | 192篇 |
2016年 | 154篇 |
2015年 | 225篇 |
2014年 | 260篇 |
2013年 | 302篇 |
2012年 | 383篇 |
2011年 | 405篇 |
2010年 | 299篇 |
2009年 | 320篇 |
2008年 | 326篇 |
2007年 | 262篇 |
2006年 | 273篇 |
2005年 | 235篇 |
2004年 | 199篇 |
2003年 | 172篇 |
2002年 | 127篇 |
2001年 | 99篇 |
2000年 | 145篇 |
1999年 | 187篇 |
1998年 | 123篇 |
1997年 | 109篇 |
1996年 | 103篇 |
1995年 | 78篇 |
1994年 | 79篇 |
1993年 | 51篇 |
1992年 | 38篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有6255条查询结果,搜索用时 15 毫秒
111.
Zihao Zhang Zirong He Nan Wang Fengmei Wang Chongyu Du Jiafeng Ruan Qin Li Dalin Sun Fang Fang Fei Wang 《Advanced functional materials》2023,33(27):2214648
Rechargeable aqueous zinc batteries are promising energy storage devices because of their low cost, high safety, and high energy density. However, their performance is plagued by the unsatisfied cyclability due to the dendrite growth and hydrogen evolution reaction (HER) at the Zn anode. Herein, it is demonstrated that the concentrated hybrid aqueous/non-aqueous ZnCl2 electrolytes constitute a peculiar chemical environment for not only the Zn-ions but also water molecules. The high concentration of chloride ions substitutes the H2O molecular in the solvation structure of Zn2+, while the acetonitrile further interacts with H2O to decrease its activity. The hybrid electrolytes both inhibit the dendrite formation and HER, enabling an ultrahigh average Coulombic efficiency of 99.9% in the Zn||Cu half-cell and a highly reversible Zn plating/stripping with a low overpotential of 21 mV. Using this hybrid electrolyte, the Zn||polytriphenylamine (PTPAn) full cell deliveres a high discharge capacity of 110 mAh g−1, a high power density of 9200 W kg−1 at 100 °C and maintains 85% of the capacity for over 6000 cycles at 10 °C. This study provides a deep understanding between the solvation structure and columbic efficiency of Zn anode, thus inspiring the development for stable Zn batteries. 相似文献
112.
在探测能力、波形设计及天线指向等因素制约下,分布式雷达视场并非完全重合,由此造成的观测信息差异给后续信息融合带来了巨大挑战。该文基于高斯混合实现的集势概率假设密度(CPHD)滤波器,提出了一种视场部分重叠下的分布式雷达多目标跟踪方法。首先,利用多目标密度乘积切分出概率假设密度(PHD)中表征共同观测信息的部分;之后,标准的分布式融合(算术平均或几何平均融合)方法作用于切分出的共同观测目标信息以提升跟踪性能,补偿融合则作用于雷达单独观测目标信息以扩展视场范围。该文方法无须视场先验信息,能够适应雷达视场未知时的分布式融合多目标跟踪场景。仿真实验验证了所提出方法在未知、时变雷达视场下跟踪多目标的性能,表明了该文方法比基于高斯混合的聚类方法性能更好。 相似文献
113.
重复累积(RA)码是一种特殊结构的低密度奇偶校验(LDPC)码,不仅具有LDPC码的优点,还能实现差分编码。针对LDPC编码协作系统编码复杂度高、时延长的问题,该文引入准循环RA(QC-RA)码,推导出信源节点和中继节点采用的QC-RA码对应的联合校验矩阵,基于公差构造方法设计该联合校验矩阵,并证明该方法设计的联合校验矩阵不存在围长为girth-4, girth-6的短环。理论分析和仿真结果表明,同等条件下该系统比相应点对点系统具有更优异的误码率性能。仿真结果同时表明,与采用一般构造QC-RA码或基于Z型构造QC-RA码相比,采用基于公差构造的联合设计QC-RA码的多信源多中继协作均可获得更高的编码增益。 相似文献
114.
Yongfeng Guo Li Wang Guowei Zhang Pengju Hou 《Materials and Manufacturing Processes》2017,32(3):294-301
In this study, electrical discharge machining has been used to machine insulating zirconia via the assisting electrode method. The process parameter optimization was investigated by combining the Taguchi method with grey relational analysis. The application of Taguchi–grey relational analysis is proven to effectively improve the performance of electrical discharge machining in drilling insulating zirconia. The results of this analysis indicate that the final optimal process parameters are a peak current of 8 A, a pulse duration of 16?µs, a duty cycle of 0.5, and a flushing pressure of 6?MPa. Additionally, the material removal rate, electrode wear rate, and hole taper ratio increase by 39%, 1.5%, and 1.3%, respectively, which improves the grey relational grade by 6.8%. The electrical resistance test confirms that the conductivity of the conductive layer obtained using the final optimal process parameters is better than that of the conductive layer obtained using the initial optimal process parameters. Energy spectrum analysis reveals that the conductive layer is composed of C, Cu, Zn, Zr, and O. Analysis of variance shows that the most significant component of the multi-responses is the peak current, with a 51.4% contribution. 相似文献
115.
Tuning Surface Structure and Strain in Pd–Pt Core–Shell Nanocrystals for Enhanced Electrocatalytic Oxygen Reduction
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
116.
117.
118.
为了探讨熔融成型桌面打印机成型的基础几何尺寸精度,并为熔融成型桌面打印机的市场定位提供设计参考依据,设计了线纹、步距、间隙、孔径、台阶等典型几何特征的三维模型,并采用选用PLA材料对这些基础几何特征进行熔融沉积成型。实验分别在自组装FDM 3D打印机、厦门螺壳电子科技有限公司、浙江闪铸三维科技有限公司的标准打印机上实施。最后基于对FDM成型的标准版基础几何特征尺寸精度能力的测试,初步提出一些适用于FDM打印品的质量评价方法以及标准测试样板的设计规则,对3D打印机的市场定位以及建立相关标准提供第三方检验测试手段。 相似文献
119.
Biwei Deng Rong Xu Kejie Zhao Yongfeng Lu Sabyasachi Ganguli Gary J. Cheng 《Materials Today》2018,21(5):467-474
Manufacturing ultralight and mechanical reliable materials has been a long-time challenge. Ceramic-based mechanical metamaterials provide significant opportunities to reverse their brittle nature and unstable mechanical properties and have great potential as strong, ultralight, and ultrastiff materials. However, the failure of ceramics nanolattice and degradation of strength/modulus with decreasing density are caused by buckling of the struts and failure of the nodes within the nanolattices, especially during cyclic loading. Here, we explore a new class of 3D ceramic-based metamaterials with a high strength–density ratio, stiffness, recoverability, cyclability, and optimal scaling factor. Deformation mode of the fabricated nanolattices has been engineered through the unique material design and architecture tailoring. Bending-dominated hollow nanolattice (B-H-Lattice) structure is employed to take advantages of its flexibility, while a few nanometers of carbonized mussel-inspired bio-polymer (C-PDA) is coherently deposited on ceramics’ nanolayer to enable non-buckling struts and bendable nodes during deformation, resulting in reliable mechanical properties and outperforming the current bending-dominated lattices (B-Lattices) and carbon-based cellulose materials. Meanwhile, the structure has comparable stiffness to stretching-dominated lattices (S-Lattices) while with better cyclability and reliability. The B-H-Lattices exhibit high specific stiffness (>106?Pa·kg?1·m?3), low-density (~30?kg/m3), buckling-free recovery at 55% strain, and stable cyclic loading behavior under up to 15% strain. As one of the B-Lattices, the modulus scaling factor reaches 1.27, which is lowest among current B-Lattices. This study suggests that non-buckling behavior and reliable nodes are the key factors that contribute to the outstanding mechanical performance of nanolattice materials. A new concept of engineering the internal deformation behavior of mechanical metamaterial is provided to optimize their mechanical properties in real service conditions. 相似文献
120.
Thomas Guillemet Jean‐Marc Heintz Bruno Mortaigne Yongfeng Lu Jean‐François Silvain 《Advanced Engineering Materials》2018,20(1)